Influence of sex and degree of prematurity on the heart structure in the late postnatal period of ontogenesis

Abstract

BACKGROUND: People born prematurely have an increased risk of early heart disease. However, to date, based on the results of clinical studies, drawing a clear conclusion about the influence of sex and degree of prematurity on the structure of the heart of people born prematurely is impossible. Experimental studies aimed at identifying the structural features of the myocardium of preterm animals depending on the sex and degree of prematurity are relevant. AIM: To present the morphological characteristics of the left ventricle of preterm rats on days 42–180 of the postnatal period of ontogenesis, taking into account sex and degree of prematurity. MATERIALS AND METHODS: The study was conducted on full-term, 12- and 24-h preterm male and female Wistar rats. Each group included 24 animals, including 12 males and 12 females. To obtain premature rat offspring, preterm birth was induced by antiprogestin mifepristone (10 mg/kg) injection. Histological and immunohistochemical studies of the left ventricle of premature male and female rats were performed on days 42, 56, and 180 of the postnatal period of ontogenesis. The following parameters were determined in the left ventricular wall: wall thickness, diameter and relative volume of the cardiomyocytes, and number of caspase 3-positive cardiomyocytes in 1 mm2 of the myocardium. RESULTS: The left ventricular wall of preterm and full-term animals on days 42–180 of the postnatal period of ontogenesis has a fundamentally similar structure. However, preterm birth, regardless of sex, leads to a decrease in the relative volume of left ventricular cardiomyocytes. On day 56 of the postnatal period of ontogenesis, the number of caspase 3-positive cardiomyocytes increased only in male rats with a greater degree of prematurity. CONCLUSION: Preterm birth influenced the relative volume of the cardiomyocytes and number of caspase 3-positive cardiomyocytes of the left ventricle; however, the influence of sex and degree of prematurity on these parameters is unclear. An earlier increase in the number of caspase 3-positive cardiomyocytes in the left ventricle of rats born 24 h preterm indicates the different adaptive potential of the myocardium of animals with different degrees of prematurity. The results of the study suggest a cardioprotective effect of female sex steroids in premature animals.